The invention relates to a cochlear implant, comprising a signal processor, having a set of audio channel units and being provided for the conversion of sound signals, according to a frequency related tonotopic division, each audio channel being provided for applying a frequency related filtering to said sound signal, each audio channel having an output associated with a first sampling unit, provided for sampling at an audio channel associated sampling rate, the signal output by its associated audio channel unit and writing sampled signal values into a storage buffer, each sampling unit being connected with said storage buffer, provided for temporarily storing said sampled signal values, said storage buffer being connected with a waveform generator comprising at least one stimulation channel, said waveform generator and said storage buffer being connected to a read signal generator, is provided for generating read signals enabling to read the stored sampled signal values from said storage buffer, said waveform generator being provided for retrieving under control of said read signal, said sampled signal values of each audio channel from said storage buffer and for generating based on said sampled signal values waveforms having a time period and a wave pattern, said waveform generator being provided for stimulating by means of said waveforms electrode contacts of said cochlear implant.
A cochlear implant is well known and is used to restore auditory perception, at least partially, to the deaf and hard-of-hearing. Cochlear implants make it possible to create auditory sensation, by generating electric field gradients in the area of the peripheral nerve fibres of the auditory nerve bundle. This bundle contains approximately 30,000 individual afferent nerve fibres, normally linked to approximately 4,500 internal hair cells. The sound signals are picked up by a microphone, converted into digital signals, and processed by the signal processor in order to activate different stimulation channels, which stimulate different groups of nerve fibres of the auditory nerve. The area where the initialisation of action potentials takes place is referred to as the excitation area. The initialisation site of the action potential can be located either in the dendrites, at the site of the cell body, at the level of the axons or any combination. To ensure that each stimulation channel doesn""t lack essential information, due to the different timings in writing by the signal processor and reading by the waveform generator, the buffer is implemented as a temporal peak hold storage.
A drawback of the known cochlear implants is that there is no clear distinction between sound processing part and stimulation channels. As a result, the stimulation strategy i.e. the manner according to which the various stimulation channels are activated, cannot be chosen independently of the signal processing.
It would therefore be advantageous to provide a cochlear implant, which enables a strategy which takes into account the patient dependent data, the case history (like temporal field interaction) and the electric field interaction during simultaneous stimulation of different stimulation channels.
For this purpose a cochlear implant is characterised in that said signal processor comprises a stimulation channel configuration unit connected with said storage buffer and provided for configurating stimulation channels in order to create electrical fields along auditory neural structures, said stimulation channel configuration unit being connected to said electrode contacts and further provided to allocate to each stimulation channel at least two of said electrode contacts, to each stimulation channel there being assigned a memory element provided for storing a waveform platform and a wave duration according to and during which an intensity value determined on the basis of the sampled signal value attributed to the considered stimulation channel is applicable to the electrode contacts allocated to the considered stimulation channel, said memory element being further provided for storing a maximum value for said intensity value indicating a maximum field strength for the considered stimulation channel and a first and second field identifier identifying a field spread in a basal and apical direction relative to a position of the stimulation channel.
In order to carry through the best possible conversion of the stored sampled signal values, into current or voltage stimulation waveforms for the N different stimulation channels, it is necessary to determine a suitable stimulation strategy. This strategy should take into account the patient-dependent data, the case history (like temporal field interaction) and the electric field interaction during simultaneous stimulation of different stimulation channels. In order to take this into account a cochlear implant according to the invention comprises M (M greater than 1) electrode contacts and a signal processor having a set of N audio channel units and being provided for the conversion, according to a frequency related tonotopic division, of sound signals, each audio channel being provided for applying a frequency related filtering to said sound signal, each audio channel having an output associated with a second sampling unit provided for sampling at an audio channel associated sampling rate the signal output by its associated audio channel unit and writing them into a storage buffer, each second sampling unit being connected with said storage buffer provided for temporarily storing sampled signal values supplied by its associated second sampling unit.
Such a cochlear implant is characterised in that said storage buffer is connected with a stimulation channel configuration unit, provided for defining stimulation channels in order to create electrical fields along auditory neural structures, said stimulation channel configuration unit being further provided to allocate to each stimulation channel at least two of said electrode contacts, to each stimulation channel a memory element is assigned, provided for storing a waveform pattern and a wave duration according to and during which an intensity value determined on the basis of the sampled signal value attributed to the considered stimulation channel is applicable to the electrodes assigned to the considered stimulation channel, said memory element being further provided for storing a maximum value for said intensity value indicating a maximum field strength for the considered stimulation channel and a first and second field identifier, identifying a field spread in a basal and apical direction relative to a position of the electrode contacts of the considered stimulation channel.
The stimulation channel configuration unit makes it possible to establish specific stimulation channel configurations and specific stimulation intensity values and waveforms for each patient and store them.
A second preferred embodiment of a cochlear implant according to the invention is characterised in that it comprises a stimulation sequence identifier, provided for identifying a set of groups of stimulation channels which are simultaneously stimulatable, the stimulation channels of a same group being selected in order to enable a neural stimulation at neural excitation locations which match with neural excitation locations that would be obtained if the individual stimulation channels of the group would have been stimulated sequentially in time, said stimulation sequence identifier being further provided for cyclically stimulating said groups of stimulating channels. Simultaneous stimulation of several auditory neural structures thus becomes available. In such a manner, a more efficient stimulation strategy can be obtained leading to a better audible result for the patient.
A third preferred embodiment of a cochlear implant according to the invention is characterised in that it comprises an ordering unit provided to order the groups within the set according to a sequence defining the order according to which the different groups are sequentially stimulated. By arranging the groups, a more efficient use of the stimulation channels is obtained.
Preferably, a time frame is assigned to each group of said set in such a manner, that the time frame of the assigned group is at least equal to the waveform duration of the stimulation channel within the considered group having the largest waveform duration. An efficient time sharing is thus obtained.